git-bisect is magical

Arthur C. Clarke's Third Law states: Any sufficiently advanced technology is indistinguishable from magic.

You guys have done it -- I can't distinguish git-bisect from magic. It's wonderful, and thank you!

I used it for the first time this morning to find the commit which caused some kernel breakage. I just sent off an email to the developer whose commit did the breakage, and it only took me about 45 minutes. (Now all I need to do is sit back and wait for his reply saying 'You're an idiot!')

I have one minor suggestion for howto/isolate-bugs-with-bisect.
Linus states:
       git bisect good ORIG_HEAD       <- mark ORIG_HEAD as good (or
                                           whatever other known-good
                                           thing you booted last)

Well, in my case, I new the last good kernel was *two* updates ago, so ORIG_HEAD wasn't the right thing to use. I had to guess what to type instead of 'ORIG_HEAD'.

Which leads to one more question: I have my kernel configured to add the -gxxxxxxxx localversion string to the kernel name. I took a wild guess that the xxxxxxxx was the right thing to substitute for 'ORIG_HEAD' and I got lucky. But what about someone who doesn't know the magic 'xxxxxxxx' to use? If I didn't know enough to keep a week's worth of daily kernel-builds with the 'xxxxxxxx' to guide me, would I still be able to do what I did today? (For example, if this had been a 'git' bug instead of a kernel bug, I don't think I could have figured out how to use git-bisect to find the bug -- could I?)

Thanks!